My wife is a key worker and has to commute into London everyday. She wants to avoid the tube and walk if possible. We have just spent several hours trying to understand the costs of Oyster etc.
The Oyster smartcard supports a Pay As You Go service with daily and weekly (only on linked debit/credit cards). These are not relevant to commuting.
If you know you will be going in every day for a month you must buy a Monthly ticket because these offer a huge discount on the daily price (~30%) and allow peak time travel with no extra charge.
The choices are
- A monthly Travelcard that includes rail, tube and bus
- A monthly Rail Season Ticket that is just for rail and is much cheaper (my local company is SouthEastern and they now have a smartcard like the Oyster).